164 THE DISEASES AND DISORDERS OF THE OX. 



the surface of the body in cases when internal structures are 

 inflamed, is possibly to be in part explained in this way. 



Irritation, as we have said above, may be intensified to such 

 an extent as to be nothing less than actual pain, and when this 

 is the case, all the intricate mechanism of work, of the fight, 

 may be called into action instead of small portions only of that 

 mechanism. For instance, a sheep, after all attempts to dis- 

 lodge the oestrus ovis have proved unavailing, runs about madly, 

 until well-nigh exhausted with fatigue. A man, too, may be 

 irritated by the harvest bug until he is in a semi-pyrexial state. 



Again, if a nauseous and irritating substance be swallowed, 

 vomiting may ensue. In fact, if an irritant be present in any 

 portion of the digestive tract, either vomiting or defecation, or 

 both these processes, may occur. In most instances it is with- 

 out doubt best that substances which are nauseous or irritating 

 should be thus rejected. This reflex action, however, which is 

 in these cases of such supreme importance, persists under patho- 

 logical conditions when it works harm. So alive are the intes- 

 tines to the reflex eff'ect caused by irritation that vomiting may 

 occur in enteritis, or owing to compression of a portion of gut in 

 a case of hernia. 



Vomiting may also occur if structures in close relation with 

 the intestines are injured, for instance in peritonitis, in compres- 

 sion of the mesentery in a case of hernia, in biliary colic, in 

 irritation of the fauces. So also tenesmus may be excited by 

 irritation and inflammation of the lower part of the intestines. 

 In many of these cases the reflex eff'ect is productive of harm. 

 There is reason to believe that the irritation of the throat is a 

 part cause of the vomiting which occurs at an early stage in 

 cases of scarlet fever ; and since vomiting also occurs at the onset 

 of diphtheria and small-pox, in which the fauces are attacked, 

 and also closely follows the onset of other cases of inflammation 

 of the fauces, it seems as if in all these cases the irritation were 

 the cause of the vomiting. Similarly, violent coughing may 

 bring on retching, which is apparently due to the irritation of a 

 pellet of mucus which has been coughed up into the throat. 



We may say, then, that the alimentary tract is peculiarly 

 sensitive, and that while this sensitivity in normal processes 

 does good, it may in abnormal conditions work a vast amount of 

 harm. We may also conclude that irritation, in like manner 



